Radio-frequency (RF) transmitters and receivers are used in a multiplicity of applications, particularly in the field of wireless communication and radar sensors. In the automotive field there is an increasing need for radar sensors which can be used, inter alia, in driver assistance systems (Advanced driver assistance systems, ADAS) such as e.g. in cruise control (ACC, Adaptive Cruise Control, or Radar Cruise Control) systems. Such systems can automatically adapt the speed of an automobile in order thus to maintain a safe distance from other automobiles ahead (and also other objects and pedestrians). Further applications in the automotive field are e.g. blind spot detection, lane change assist and the like.
Modern radar systems use large scale integrated RF circuits which can contain all core functions of an RF frontend of a radar transceiver in a single chip housing (single-chip transceiver). Such RF frontends can comprise, inter alia, an RF local oscillator (LO), power amplifiers, low noise amplifiers (LNAs) or mixers.
Frequency-modulated continuous-wave (FMCW) radar systems use radar signals that include sequences of so-called chirps. In order to generate such chirps, the radar device can comprise a local oscillator comprising a VCO arranged in a phase-locked loop (PLL). The frequency of the VCO is set by way of a control voltage, which can be tuned by adapting the frequency division ratio of a frequency divider in the feedback loop of the PLL. In order to keep the phase noise of the local oscillator output signal within specified limits, the bandwidth of the PLL can be designed in accordance with these specified limits. However, the bandwidth of the PLL is generally dependent on parameters that are subject to a certain variation on account of tolerances in the production process.